(Maint) Update the supported ruby versions

The list of ruby versions was incorrect (1.8.5 is no longer supported)
and unclear (there is no best effort support of other versions). This
simplifies the language there.
(Maint) Point users to mailing list and IRC
(Maint) Remove "RVM considered harmful"

Many of the developers on puppet actually use RVM for developing. There
is no need to call it out in this manner.
(Maint) Remove references to 'I'

There is no 'I' in this document. Removing the first person allows us to
be more direct in the language used for expressing things.
(Maint) Create sections of information

Try to group things a little better into sections.
(Maint) Change to README.md for yard frontpage

The README.md presents a much better intro into what puppet is, whereas
the the README_DEVELOPER.md gets much more in depth in issues and
gotchas.
Merge pull request #1377 from zaphod42/maint/master/update-readmes

(Maint) Update README.md and README_DEVELOPER.md